High-Throughput Nanoelectrospray Ionization-Mass Spectrometry Analysis of Microfluidic Droplet Samples

Abstract

Droplet microfluidics enables high-throughput manipulation of fL−μL volume samples. Methods implemented for the chemical analysis of microfluidic droplets have been limited in scope, leaving some applications of droplet microfluidics difficult to perform or out of reach entirely. Nanoelectrospray ionization-mass spectrometry (nESI-MS) is an attractive approach for droplet analysis, because it allows rapid, label-free, information-rich analysis with high mass sensitivity and resistance to matrix effects. Previous proof-of-concept systems for the nESI-MS analysis of droplets have been limited by the microfluidics used so that stable, long-term operation needed for high-throughput applications has not been demonstrated. We describe a platform for the stable analysis of microfluidic droplet samples by nESI-MS. Continuous infusion of droplets to an nESI emitter was demonstrated for as long as 2.5 h, corresponding to analysis of over 20 000 samples. Stable signal was observed for droplets as small as 65 pL and for throughputs as high as 10 droplets/s. A linear-concentration-based response and sample-to-sample carryover of <3% were also shown. The system is demonstrated for measuring products of in-droplet enzymatic reactions.

How electrospray potentials can disrupt droplet microfluidics and how to prevent this

“…In droplet microfluidics, usually only the disperse polar, mostly aqueous phase is electrically conductive, so it is necessary to consider how the electrical potential can be transferred from the emitter to the droplets. The easiest way to realize this is to implement an electrically conductive capillary emitter which is compatible with capillarybased droplet systems [11][12][13][14][15][16][17] as well as with polymer chip devices.…”

Recent advances in high-throughput mass spectrometry that accelerates enzyme engineering for biofuel research

“…These droplets can be directly interfaced to an ESI source for MS-based screening at a rate of < 1 s ( Fig. 1b) [24,29]. To achieve robust screening, it is necessary to perform systematic optimization of many parameters including flow rate, emitter configuration, and droplet-stabilizing surfactants [29].…”

“…1b) [24,29]. To achieve robust screening, it is necessary to perform systematic optimization of many parameters including flow rate, emitter configuration, and droplet-stabilizing surfactants [29]. For microfluidic droplets, it is also possible to combine optical and MS screening in a single lab-on-a-chip platform to provide complementary information [35].…”

A Droplet Microfluidic Platform for High-Throughput Photochemical Reactions

“…In this work, we aimed to develop a system for irradiating droplet samples, followed by in-line dilution and subsequent electrospray ionization mass spectrometry (ESI-MS) analysis ( Figure 1). Droplet samples (5-10 nL) were generated from a standard 384 or 1536 microwell plate using previously reported methods (21)(22)(23)(24), enabling the facile translation of a wide variety of reaction conditions into droplet format. In our preliminary studies, we constructed an easily assembled, low-footprint photoreactor (25).…”